Flame retardant compositions

ABSTRACT

A composition useful in the manufacture of cable comprising:     (i) a copolymer comprised of ethylene and vinyl acetate; (ii) a surface treated magnesium hydroxide having (a) a strain in the &lt;101&gt; direction of not more than 3.0 X 10&lt;-&gt;&lt;3&gt;; (b) a crystallite size in the &lt;101&gt; direction of more than 800 angstroms; and (c) a surface area, determined by the BET method, of less than 20 square meters per gram; and   (iii) a silicone fluid. l

TECHNICAL FIELD

This invention relates to flame retardant compositions containing anethylene copolymer and a magnesium hydroxide filler. The compositionsare particularly useful in plenum cable.

BACKGROUND ART

Plenum cable is used to carry power through ducts which are used toventilate, for example, high-rise buildings. While a fire occurring inthese ducts can be dangerous in its own right, such a conflagration isespecially insidious because the smoke and other gases resulting fromthe fire are transported through the ducts throughout the building, evento parts quite remote from the blaze. In some cases, colorless andodorless gases can invade sleeping quarters housing unsuspecting people.

The cable used in plenums is generally constructed of metal conductorsinsulated with a polymeric material. These elements are generallytwisted to form a core and are protected by another Polymeric sheath orjacket material. In certain cases, added protection is afforded byinserting a wrap between the core and the sheath.

To mitigate the dangers of a duct fire, it is important that the cablejacketing is not only flame retardant, but, on burning, produces aminimum amount of smoke, emits low levels of corrosive gases and isself-extinguishing. Further, the cable should not raise installationproblems caused by materials, which are toxic to the touch.

Ethylene polymers are considered to be deficient insofar as flameretardance or flame resistance is concerned. One method for increasingflame resistance in these polymers is to formulate using metalhydroxides as the flame retardant additive. Both aluminum hydroxide andmagnesium hydroxide have been used in this way. Generally, thesehydroxides are viewed as equivalents as flame retardants in thiscontext. Aluminum hydroxide is preferred on a cost/performance basis,however. Thus, more than ninety-five percent of all hydrate basedcommercial formulations use aluminum hydroxide.

In spite of the cost advantage of aluminum hydroxide, there is a strongthrust towards improving the flame resistance of plenum cable as well asits smoke, corrosion, self-extinguishing, and toxic characteristicsbecause of the vulnerability of the occupants of buildings containingplenums through which air is transported for heating and cooling.

DISCLOSURE OF INVENTION

An object of this invention, therefore, is to provide a compositionbased on a polymer of ethylene, which can be used as jacketing forplenum cable and will furnish the plenum cable with superior flameretardance or resistance, low smoke and corrosive gases emissions, aself-extinguishing characteristic, and essentially no handling toxicity.

Other objects and advantages will become apparent hereinafter.

According to the invention, a composition has been discovered, whichmeets the above objective. The composition comprises:

(i) a copolymer comprised of ethylene and vinyl acetate;

(ii) magnesium hydroxide having (a) a strain in the <101> direction ofno more than 3.0×10⁻³ ; (b) a crystallite size in the <101> direction ofmore than 800 angstroms; and (c) a surface area, determined by the BETmethod, of less than 20 square meters per gram, said magnesium hydroxidehaving been surface treated with one or more carboxylic acids having 8to 24 carbon atoms or the metal salts thereof; and

(iii) a silicone fluid.

DETAILED DESCRIPTION

Copolymers comprised of ethylene and vinyl acetate are well known andcan be prepared by conventional techniques. The portion of the copolymerattributed to the vinyl acetate monomer can be in the range of about 12to about 60 parts by weight based on 100 parts by weight of thecopolymer and is preferably in the range of about 25 to about 52 partsby weight.

The magnesium hydroxide defined above and a method for its preparationare disclosed in U.S. Pat. No. 4,098,762 issued on Jul. 4, 1978. Apreferred characteristic of the magnesium hydroxide is that the surfacearea, as determined by the BET method, is less than 10 square meters pergram.

The amount of magnesium hydroxide used in the composition is in therange of about 50 to about 350 parts by weight of magnesium hydroxideper one hundred parts by weight of ethylene/vinyl acetate copolymer andis preferably in the range of about 75 to about 250 parts by weight ofmagnesium hydroxide per one hundred parts by weight of ethylene/vinylacetate copolymer.

The magnesium hydroxide is preferably surface treated with a saturatedor unsaturated carboxylic acid having 8 to 24 carbon atoms andpreferably 12 to 18 carbon atoms or a metal salt thereof. Mixtures ofthese acid and/or salts can be used, if desired. Examples of suitablecarboxylic acids are oleic, stearic, palmitic, isostearic, and lauric;of metals which can be used to form the salts of these acids are zinc,aluminum, calcium, magnesium, and barium; and of the salts themselvesare magnesium stearate, zinc oleate, calcium palmitate, magnesiumoleate, and aluminum stearate. The amount of acid or salt can be in therange of about 0.1 to about 5 parts by weight of acid and/or salt perone hundred parts by weight of magnesium hydroxide and preferably about0.25 to about 3 parts by weight per one hundred parts by weight ofmagnesium hydroxide. The acid or salt can be merely added to thecomposition in like amounts rather than using the surface treatmentprocedure, but this is not preferred.

Component (iii) is a silicone fluid. Silicone fluids are organosiloxanepolymers commercially available in a range of viscosities from 0.65 toabout 1,000,000 centistokes. Viscosities in the range of about 1000 toabout 1,000,000 centistokes are useful in subject composition and thosein the range of about 10,000 to about 1,000,000 centistokes arepreferred. The silicone fluids can be saturated or unsaturated. Theunsaturated silicone fluids, of particular interest, are those havingone or more ethylenically unsaturated groups, e.g., those which arevinyl substituted. These silicone fluids can contain about 1 to about 10percent by weight ethylenically unsaturated groups and preferablycontain about 2.5 to about 7 percent by weight ethylenically unsaturatedgroups.

One embodiment of a silicone fluid can be represented by the followingformula: ##STR1## wherein R can be CH₂ ═CH--or CH₃ --and x plus y can beequal to 1 to 5000. The silicone fluids are preferably characterized bytheir viscosity, however.

The amount of silicone fluid which can be used in subject composition isin the range of about 0.1 to about 10 parts by weight of silicone fluidper one hundred parts by weight of polymer and is preferably in therange of about 1 to about 5 parts by weight per one hundred parts byweight of polymer.

Other useful additives for the plenum cable composition are couplingagents, surfactants, free radical generators, reinforcing filler orpolymer additives, antioxidants, ultraviolet stabilizers, antistaticagents, pigments, dyes, slip agents, plasticizers, lubricants, viscositycontrol agents, extender oils, metal deactivators, water tree growthretardants, voltage stabilizers, flame retardant additives, and smokesuppressants. Some of the more important additives are discussed below.

A coupling agent is a chemical compound, which chemically binds polymercomponents to inorganic components. This is effected by a chemicalreaction taking place at the temperatures under which the formulation iscompounded, about 70° C. to about 180° C. The coupling agent generallycontains an organofunctional ligand at one end of its structure whichinteracts with the backbone of the polymeric component and a ligand atthe other end of the structure of the coupling compound which attachesthrough reaction with the surface of the filler. The following silanecoupling agents are useful in subject composition:gamma-methacryloxypropyltrimethoxy silane; methyltriethoxy silane;methyltris (2-methoxyethoxy) silane; dimethyldiethoxy silane;vinyltris(2-methoxyethoxy) silane; vinyltrimethoxy silane; andvinyltriethoxy silane; and mixtures of the foregoing. A preferred silanecoupling agent is a mixture of gamma-methacryloxypropyltrimethoxy silaneand vinyltriethoxysilane. This mixture is described in U.S. Pat. No.4,481,322.

Useful reinforcing additives include polymerizable unsaturated organiccompounds having at least two polymerizable unsaturated groups. It isbelieved that the reinforcing additive reacts chemically with thethermoplastic polymer matrix during the hot melt compounding of thefilled thermoplastic polymer. It is further believed that thereinforcing additive causes the formation of a strong and toughinterphase between the individual filler particles and the surroundingmatrix polymer, enabling the polymer to withstand the local stressconcentrations caused by the filler particles, which might otherwiseresult in matrix crack initiation and catastrophic failure. It isbelieved that such increases in the toughness of the interphase enablethe simultaneous achievement of high stress and ductility in the finalcomposite. Filler treatments which rely solely on increased adhesion,i.e., coupling, between the filler surface and the matrix polymer, canincrease the composite strength, but, if there is no improvement ininterphase toughness, the composite will remain brittle. This concept isdiscussed in U.S. Pat. No. 4,385,136. The reinforcing additives includeany organic compounds of the above description which do not contain anygroup or element adversely affecting the function of the polymer;filler; silane; or any other component of the composition. Suitableunsaturated organic compounds include ester diol 2,4-diacrylate, 1,4butylene glycol diacrylate, diethylene glycol dimethacrylate,triallyl-s-triazine-2,4,6-(1H, 3H, 5H)-trione, triallyl mellitate,pentaerythritol triacrylate, polycaprolactone triacrylate, m-phenylenebis maleimide, dipentaerythritol pentaacrylate, melamine triacrylate,epoxidized linseed oil/acrylate, triacryloyl hexahydro-s-triazine,trimethylolpropane trimaleate, trimethacryloyl hexahydro-s-triazine,N,N-tetraacryloyl 1,6-diaminopyridine, 1,3-butylene glycoldimethacrylate, 1,3-butylene glycol diacrylate, ethylene glycoldimethacrylate, ethylene glycol diacrylate, diethylene glycoldiacrylate, triethylene glycol diacrylate, polyethylene glycoldimethacrylate, polyethylene glycol diacrylate, trimethylol propanetrimethacrylate, trimethylol propane triacrylate, divinyl sulfone,dicyclopentadiene, bisalkyl glycol dicarbonate, triallyl cyanurate,acetyl triallyl citrate, divinyl benzene, dialkyl pthalate, tetraallylmethylenediamine, tetraallyl oxyethane, 3-methyl-1,4,6-heptatriene;1-10-decamethylene glycol dimethacrylate and di-, tri-, tetra-, andpenta-acrylates of poly(vinyl alcohol). In addition, the following lowmolecular weight polyunsaturated polymers may be used: polybutadieneoligomers, hydroxyl terminated polybutadiene oligomers, hydroxylterminated styrene-butadiene and acrylonitrilebutadiene oligomers,unsaturated polyesters, and partial alkyl esters of styrene-maleicanhydride oligomers.

It is preferred to employ polymerizable unsaturated organic compoundsthat have a high unsaturated level to molecular weight ratio. Therefore,the tri-, tetra-, and penta-acrylates of poly(vinyl alcohol) and theother tri-, tetra-, and penta-acrylates and methacrylates of polyolssuch as pentaerythritol, methylolpropane, and dipentaerythritol, asdescribed above, are preferred.

The coupling agent and reinforcing additive are each used in amounts ofabout 0.05 part by weight to about 0.5 part by weight for each 100 partsby weight of copolymer. The effect can be maximized by the inclusion ofsuitable surfactants and free radical generators.

Examples of antioxidants are: hindered phenols such astetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methaneand thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate;phosphites and phosphonites such astris(2,4-di-tert-butylphenyl)phosphite anddi-tert-butylphenylphosphonite; various amines such as polymerized2,2,4-trimethyl-1,2-dihydroquinoline; and silica. A tetrakis methanecompound is preferred. Antioxidants are used in amounts of about 1 toabout 5 parts by weight per hundred parts by weight of copolymer.

The patents mentioned in this specification are incorporated byreference herein.

The invention is illustrated by the following examples.

EXAMPLES 1 to 16

The magnesium hydroxide used in the examples is prepared as follows:

Five liters of an aqueous solution of magnesium chloride having aconcentration of 1.5 moles per liter (the temperature of the solution is15° C.) is placed in a reaction vessel having a capacity of about 10liters, and the solution is stirred. An ammonia solution with aconcentration of 10 moles per liter (the temperature of the solution is15° C.) is added in an amount of 1.35 liters (corresponding to 0.9equivalent of the magnesium chloride, i.e., per equivalent of magnesiumchloride) over the course of about 10 minutes.

A part of the resulting suspension is immediately filtered at reducedpressure, and then washed thoroughly with water and then with acetone.The product is dried for about 2 hours at room temperature, and analyzedby X-ray diffraction and by a chemical analysis method. By the X-raydiffraction, the product is identified as basic magnesium chloridehaving the structure defined for the magnesium hydroxide. The chemicalanalysis shows that this product has the composition Mg(OH)₁.903Cl₁₀.097 mH₂ O. The presence of water of crystallization was confirmedby DTA and TGA. Immediately after the reaction, a greater portion of theremaining suspension is placed in a 20-liter autoclave, andhydrothermally treated at 180° C. for 8 hours. This heat treatment iscarried out within about 2 hours after the end of the reaction becausethis unstable substance has to be treated while it remains undecomposed.After the hydrothermal treatment, the product is filtered at reducedpressure, washed with water and dried. The product obtained isidentified as magnesium hydroxide by X-ray diffraction. It has a strainin the <101> direction of 0.970×10⁻³, a crystallite size in the <101>direction of 4200 angstroms, and a specific surface area by the BETmethod of 6.7 square meters per gram.

DTA=differential thermal analysis

TGA=thermal gravimetric analysis

BET method=a nitrogen adsorption surface area measurement

Sixteen compositions are processed into test specimens as required bythe test procedure for Limiting Oxygen Index (LOI), i.e., ASTM-D2863-70, and the test procedure is carried out. See, also, U.S. Pat. No.4,446,279 issued May 1, 1984. Limiting Oxygen Index measures andquantifies flame resistance. The higher the LOI number the greater theflame resistance or flame retardance and the lower the emissions ofsmoke and other harmful gases. It is observed that no corrosive gasesare present in the emissions; that the samples are self-extinguishingwithin a reasonable time; and that handling the samples provides notoxic effects on the skin.

Components in parts by weight, Limiting Oxygen Index (LOI), tensilestrength, and elongation are given in the Table.

Examples 4, 10, 13 and 14 to 16 are examples using the composition ofthe invention.

Notes accompanying the Table:

EVA=copolymer of ethylene and vinyl acetate. EVA I is based on 28percent by weight vinyl acetate. EVA II is based on 18 percent by weightvinyl acetate.

EEA=copolymer of ethylene and ethyl acrylate based on 35 percent byweight ethyl acrylate.

Polyethylene=a copolymer of ethylene and 1-butene having a density of0.905 g/cc.

Mg(OH)₂ =magnesium hydroxide prepared as above. It is surface treatedwith about 2 parts by weight of stearic acid. Parts by weight of surfacetreating acid is based on 100 parts by weight of the metal hydrate.

Silicone fluid=vinyl modified polydimethylsiloxane having a specificgravity of 0.97@25/25° C. and a viscosity of 50,000 to 70,000centistokes.

Antioxidant=pentaerythritol tetrakis (3,5-di-tert-butyl-4-hydroxyphenylpropionate).

Tensile strength (psi) is determined under

Elongation (%) is determined under ASTM D-412.

                                      TABLE                                       __________________________________________________________________________    (Parts by Weight)                                                             __________________________________________________________________________               Examples                                                                      1    2    3    4    5    6    7    8                               __________________________________________________________________________    EVA I      100  --   --   100  --   --   100  --                              EVA II     --   --   --   --   --   --   --   --                              EEA        --   100  --   --   100  --   --   100                             Polyethylene                                                                             --   --   100  --   --   100  --   --                              Mg(OH).sub.2                                                                             100  100  100  100  100  100  100  100                             Silicone Fluid                                                                           --   --   --   4.0  4.0  4.0  --   --                              Magnesium Stearate                                                                       --   --   --   --   --   --   1.0  1.0                             Antioxidant                                                                              0.4  0.4  0.4  0.4  0.4  0.4  0.4  0.4                             LOI        32   27   27   56   28   30   32   27                              Tensile Strength (psi)                                                                   1202 268  1285 1663 244  1181 1011 262                             Elongation (%)                                                                           759  321  755  731  215  724  752  269                             __________________________________________________________________________               Examples                                                                      9    10   11  12   13   14   15   16                               __________________________________________________________________________    EVA I      --   100  --  --   --   50   100  100                              EVA II     --   --   --  --   100  --   --   --                               EEA        --   --   100 --   --   --   --   --                               Polyethylene                                                                             100  --   --  100  --   50   --   --                               Mg(OH).sub.2                                                                             100  100  100 100  100  100  150  100                              Silicone Fluid                                                                           --   4.0  4.0 4.0  2.0  2.0  2.0  8.0                              Magnesium Stearate                                                                       1.0  1.0  1.0 1.0  --   --   --   --                               Antioxidant                                                                              0.4  0.4  0.4 0.4  0.4  0.4  0.4  0.4                              LOI        27   57   29  32   51   47   65   56                               Tensile Strength (psi)                                                                   1340 1742 237 1239 1388 1166 1039 1509                             Elongation (%)                                                                           754  712  168 762  640  651  688  672                              __________________________________________________________________________

I claim:
 1. A composition useful in the manufacture of cable comprising:(i) a copolymer comprised of ethylene and vinyl acetate; (ii) magnesium hydroxide having (a) a strain in the <101> direction of not more than 3.0×10⁻³ ; (b) a crystallite size in the <101> direction of more than 800 angstroms; and (c) a surface area, determined by the BET method, of less than 20 square meters per gram, said magnesium hydroxide having been surface treated with one or more carboxylic acids having 8 to 24 carbon atoms or the metal salts thereof; and (iii) a silicone fluid.
 2. The composition defined in claim 1 wherein the portion of the copolymer attributed to the vinyl acetate is in the range of about 12 to about 60 parts by weight based on 100 parts by weight of the copolymer.
 3. The composition defined in claim 1 wherein the carboxylic acids and/or metal salts thereof are present in an amount of 0.1 to about 5 part by weight based on 100 parts by weight of magnesium hydroxide.
 4. The composition defined in claim 1 wherein the silicone fluid has a viscosity in the range of about 1000 to about 1,000,000 centistokes.
 5. The composition defined in claim 4 wherein the silicone fluid has a viscosity in the range of about 10,000 to about 1,000,000 centistokes.
 6. The composition defined in claim 2 wherein the portion of the copolymer attributed to vinyl acetate is in the range of about 25 to about 52 parts by weight based on 100 parts by weight of copolymer.
 7. The composition defined in claim 1 wherein the magnesium hydroxide is present in an amount of about 50 to about 350 parts by weight based on 100 parts by weight of the copolymer.
 8. A composition useful in the manufacture of cable comprising:(i) a copolymer comprised of ethylene and vinyl acetate wherein the portion of the copolymer attributed to the vinyl acetate is in the range of about 12 to about 60 parts by weight based on 100 parts by weight of the copolymer; and (ii) magnesium hydroxide having a surface area, as determined by the BET method, of less than 10 square meters per gram, the amount of magnesium hydroxide being in the range of about 50 to about 350 parts by weight based on 100 parts by weight of the copolymer, said magnesium hydroxide being surface treated with at least one carboxylic acid having 8 to 24 carbon atoms or a metal salt thereof in an amount of about 0.1 to about 5 parts by weight based on 100 parts by weight of the magnesium hydroxide; and (iii) a silicone fluid having a viscosity in the range of about 1,000 to about 1,000,000 centistokes.
 9. An article of manufacture comprising a metal core conductor and at least one layer surrounding the core comprising the composition defined in claim
 1. 10. An article of manufacture comprising a metal core conductor and at least one layer surrounding the core comprising the composition defined in claim
 8. 11. The composition defined in claim 1 additionally containing a coupling agent.
 12. The composition defined in claim 1 additionally containing a reinforcing additive. 